The present invention generally relates to a vertebral spacer to be inserted into an intervertebral space, thereby supporting the spinal column of a patient. The present invention further relates to a system and methods for implanting the vertebral spacer into the spinal column and securing the spacer therein.
The spinal column, which is the central support to the vertebrate skeleton and a protective enclosure for the spinal cord, is a linear series of vertebral bones. Intervertebral discs separate and reduce friction between adjacent vertebrae and absorb compression forces applied to the spinal column. Spinal nerves that extend from each side of the spinal cord exit the column at intervertebral forama.
A typical vertebra comprises an anterior body, and a posterior arch that surrounds the spinal cord lying within the vertebral foramen formed by the arch. The muscles that flex the spine are attached to three processes extending from the posterior arch. On the upper surface of each vertebra in a standing human, are two superior articulated processes that oppose two inferior articulated processes extending from the lower surface of an adjacent vertebra. Facets on the opposing processes determine the range and direction of movement between adjacent vertebrae, hence the flexibility of the spinal column.
The intervertebral discs include the fibrillar cartilage of the anulus fibrosus, a fibrous ring, the center of which is filled with an elastic fibrogelatinous pulp that acts as a shock absorber. The outer third of the anulus fibrosus is innervated. The entire spinal column is united and strengthened by encapsulating ligaments.
Back pain is one of the most significant problems facing the workforce in the United States today. It is a leading cause of sickness-related absenteeism and is the main cause of disability for people aged between 19 and 45. Published reports suggest that the economic cost is significant, treatment alone exceeding $80 billion annually. Although acute back pain is common and typically treated with analgesics, chronic pain may demand surgery for effective treatment.
Back pain can occur from pinching or irritation of spinal nerves, compression of the spine, vertebral shifting relative to the spinal cord axis, and bone spur formation. The most common cause of disabling back pain, however, stems from trauma to a intervertebral disc, resulting from mechanical shock, stress, tumors or degenerative disease, which may impair functioning of the disc and limit spinal mobility. In many cases, the disc is permanently damaged and the preferred treatment becomes partial or total excision.
Another cause of back injury is herniation of the intervertebral disc, wherein the gelatinous fluid of the nucleus pulposus enters the vertebral canal and pressures the spinal cord. Again, surgery is often the only method available for permanent relief from pain or the neurological damage ensuing from the pressure of fluid on the spinal cord, and requires replacement of the damaged disc.
Traumatic injury to an intervertebral disc that is not removed will frequently promote scar tissue formation. Scar tissue is weaker than original healthy tissue so that the disc will progressively degenerate, lose water content, stiffen and become less effective as a shock absorber. Eventually, the disc may deform, herniate, or collapse, limiting flexibility of the spinal column at that position. The only option is for the intervertebral disc to be partially or totally removed.
When the disc is partially or completely removed, it is necessary to replace the excised material to prevent direct contact between hard bony surfaces of adjacent vertebrae. One vertebral spacer that may be inserted between adjacent vertebrae, according to U.S. Pat. No. 5,989,291 to Ralph et al., includes two opposing plates separated by a belleville washer or a modified belleville washer. The washer functions to provide a restorative force to mimic the natural functions of the disc of providing a shock absorber and mobility between adjacent vertebrae. However, mechanical devices intended to replicate intervertebral disc function have had only limited success. An alternative approach is a xe2x80x9ccagexe2x80x9d that maintains the space usually occupied by the disc to prevent the vertebrae from collapsing and impinging the nerve roots.
Spinal fusion may be used to restrict motion occurring between two vertebrae due to spinal segmental instability. Fusing the vertebrae together, however, reduces the mechanical back pain by preventing the now immobile vertebrae from impinging on the spinal nerve. The disadvantage of such spacers is that stability is created at the expense of spinal flexibility.
Surgical procedures for replacing intervertebral disc material, rather than the fusing of the vertebrae, have included anterior approaches and posterior approaches to the spinal column. The posterior approach (from the back of the patient) encounters the spinous process, superior articular process, and the inferior articular process that must be removed before insertion of the disc replacement material into the intervertebral space. Excessive removal of the bony process triggers further degradation and impediment of the normal movement of the spine. The anterior approach to the spinal column is complicated by the internal organs that must be bypassed or circumvented to access the vertebrae.
Many intervertebral spacers require preparation of the surfaces of the adjacent vertebrae to accommodate the spacer, causing significant tissue and bone trauma. For example, chiseling or drilling of the vertebral surface may be required to prepare a receiving slot. They may also require screwing the spacer into the intervertebral space, making installation difficult and increasing trauma to the vertebral tissue. Many spacers include complex geometries and are costly to manufacture. Examples of such geometrically complex spacers are described in U.S. Pat. No. 5,609,636 to Kohrs et al., U.S. Pat. No. 5,780,919 to Zdeblick et al., U.S. Pat. No. 5,865,848 to Baker and U.S. Pat. No. 5,776,196 to Matsuzaki et al. Many of these complex spacers may require screwing the spacer into the intervertebral space, thereby making installation difficult and traumatic to the vertebral tissue.
There is a need for a vertebral spacer having a simple geometry that is easily insertable into an intervertebral space while causing minimal trauma to the surface of the vertebrae as well as the bony processes thereof. The present invention provides a vertebral spacer having a simple geometry for supporting adjacent vertebrae after excision, at least partially or wholly, of an intervertebral disc. The spacer includes a body having a lower surface and an upper surface. The lower surface will be supported by a lower vertebra; the upper surface supports the adjacent upper vertebra. The body of the vertebral spacer of the present invention, therefore, provides support between the two adjacent vertebrae and to the spinal column.
The body of the vertebral spacer of the present invention additionally has an anterior face and a posterior face extending from the lower surface. The height of the anterior face of the body may be less than, or greater than, the height of the posterior face to maintain the curvature of the spine when the vertebral spacer is inserted between two vertebrae. The body of the vertebral spacer also includes at least one guiding groove suitable for engaging with an insertion tool for delivering the vertebral spacer to an intervertebral space.
The present invention further provides a system for delivering a vertebral spacer to the spinal column of a patient, comprising an insertion tool with a channel; (b) an optional guiding tool for directing the insertion tool to a selected point of insertion of a vertebral spacer; (c) a pusher; (d) a vertebral spacer slideably disposed in the channel of the insertion tool; and (e) a cutting tool. The cutting tool can be slid into the channel of the insertion tool providing that the pusher and the vertebral spacer are not therein.
The channel of the insertion tool is configured to slideably accept any of a vertebral spacer, a pusher, a vertebral spacer, or a cutting tool. The insertion tool further comprises a spacer guide or a plurality of spacer guides for engagement with a first guiding groove or a second guiding groove of a vertebral spacer.
In one embodiment of the insertion tool the spacer guide is a flange extending from the channel. In another embodiment, the spacer guide is two opposing flanges configured to slideably engage with a first guiding groove and a second guiding groove, respectively.
In another embodiment of the insertion tool, the spacer guide is at least one rib longitudinally placed on the inner surface of the channel of the insertion tool.
Other embodiments of the insertion tool of the present invention include spacer guides that may be, but are not limited to, a segmented longitudinal rib, or a linear series of protrusions, also on the inner surface of the channel.
The present invention further provides a method for delivering a vertebral spacer to a patient, comprising the steps of inserting the insertion tool into an intervertebral space of the spinal column of a patient, engaging at least one guiding groove of a vertebral spacer with a space guide of the insertion tool, sliding a pusher into the channel of the insertion tool, advancing the pusher and thereby pushing the vertebral spacer into the intervertebral space and removing the pusher and the insertion tool from the patient.
The method of the present invention may further comprise the optional step of inserting a guiding tool into an intervertebral space for directing the insertion tool into the intervertebral space. The insertion tool may be slid along the guide tool to a selected position suitable for insertion of a vertebral spacer in the intervertebral space. The guide tool is then extracted from the insertion tool leaving the insertion tool inserted between adjacent vertebrae.
The cutting tool is optionally slid along the channel of the insertion tool to engage a vertebra and generally is used to chisel at least one vertebral space receiving slot in the vertebrae. The cutting tool is removed from the patient by sliding the cutting tool back through the channel of the insertion tool. A vertebral spacer may then be slideably engaged with the insertion tool, with a space guide on the insertion tool engaging with a guiding groove of the vertebral spacer. The pusher may be engaged and advanced along the channel, thereby delivering the vertebral spacer into the vertebral spacer receiving slot (or receiving slots) in the adjacent vertebrae. It is also contemplated that a vertebral spacer receiving slot may not be cut in the adjacent vertebrae and that the inserted vertebral spacer optionally may contact only the uncut surface of the vertebrae.
One embodiment of the method of the present invention comprises the additional step of delivering a hardening biocompatible composition to the vertebral spacer. The hardening biocompatible composition may be used, for example, to bond the vertebral spacer to an adjacent vertebra or be an osteogenic composition to promote bone growth from the adjacent vertebrae into the vertebral spacer. The hardening biocompatible composition can be, for example, an organic polymer, a mineral composition such as a hydroxyapatite-based composition, methyl methacrylate, or the like, or a combination thereof. A hydroxyapatite-based composition is especially useful in the context of the present invention for promoting osteocyte growth and bone deposition.
Various objects, features, and advantages of the invention will become more apparent upon review of the detailed description set forth below when taken in conjunction with the accompanying drawing figures, which are briefly described as follows.